Science [3 Mark Questions]

No. Mothers have no role in determining the sex of the new born. Mothers are homogametic, that is, they produce only one type of ova (22 + X). Fathers are heterogametic, that is, they produce two types of sperms, gynosperms (22 + X) and androsperms (22 + Y). If gynosperm (22 + X) fertilises the ovum (22 + X), the sex of new born will be female (44 + 2X). If androsperm (22 + Y) fuses with ovum (22 + X), the new born will be boy (44 + XY).

Human females (44 + XX) are homogametic, that is, they produce only one type of ova (22 + X). Human males are heterogametic. They produce two types of sperms (22 + X and 22 + Y) in equal proportion, that is, 50 : 50 ratio. The chance of male or female child is also 50 : 50, as there is equal chance of androsperm (22 + Y) or gynosperm (22 + X) fertilizing an ovum.

Smaller populations are at greater threat of extinction as compared to large species. This is because less number of individual in smaller population imparts lesser changes in production of genetic variations. Lack of genetic diversity makes the smaller species more prone to extinction under any dramatic changes in prevailing environmental conditions.
On the other hand, large populations exhibit more genetic diversity on which evolutionary forces act upon to make it withstand any changes in surrounding.

Though animals have a vast diversity in structures they probably do not have a common ancestry, because common ancestry may greatly limit the extent of diversity. But we can group the animals into different groups and subgroups; on the basis of certain common characters. As many of these diverse animals are inhabiting the same habitat, their evolution by geographical isolation and speciation is also not likely. Thus, a common ancestry for all the animal is not the likely theory.

Homologous structures or organs are those structures which have similar origin, similar development, similar internal structure and similar basic plan but show different external form and function, e.g., forelimbs of amphibians, reptiles, mammals and birds. Homologous structures are always have a common ancestry because otherwise there cannot be any similarity in basic plan, internal structure, development or origin. Modifications have occurred in them due to varied adaptations.